Busy signal for automatic telephone systems



April 7, :1942. B. wEs'r E-rAL BUSY SIGNAL FOR AUTOMATIC TELEPHONESYSTEMSV Filed Sept. 15A, 1939 Patented Apr. 7, 1942 UNITED STATESPA'reNTfoFFici-i BUSY SIGNAL FOR AUTOMATIC TELPONE SYSTEMS Bronson Westand Howard L. Johnson, St. Paul, Minn.; said Johnson assignor ofone-hall| of his entire right to said West Application September 15,1939, Serial No. 295,084

3 Claims.

.mal operation of the existing busy signal, or permittingthe-conversation on the busy line to be Ioverheard by the party seekingto establish a connection with the called -subscribers line.

Other objects will appear and be more fully pointed out in the followingspecification and claims In the accompanying drawing we have illustrateddiagrammatically an automatic connector switch cir`cuit,of common typewith our improved busy signal connected thereto to operate automaticallyunder control of the busy relay.

Referring to the drawing, our special tone machine or generator isindicated by the numeral 3 in circuit with a condenser 4 and contactsprings 5. B and 1.v This circuit is connected by a wire 8 to a portionof the transmission line 9 extending to one of the Wipers I0 of the linebank fior the circuit Il of the called telephone. The wiper I0 ispreferably the ring or negative side of the circuit, the tip or positiveside being indicated by the numeral I2. The connector switch has theusual busy relay I3 and the Contact springs 5, 6 and 'I are so 'arrangedrelative to an armature of the relay I3, that the circuit including wireIl is made and then broken, after a brief interval, when this relay isenergized. Contact-is rst made between the springs 5 and 6 and as themotion of the armature continues, the spring 6 is drawn away from thespring 'I- until the .contact is broken, the spring I following thespring 6 for a brief interval of time before the break. Duringthis-interval the tone machine 3 is operative tol notify the user of theline II that a third party is attempting to call his line. When -suchthird party attempts to call the line II by operation of a duplicateautomatic connector' switch like that illustrated in the drawing, thecoil of Ibusy relay I3 is energized in the usual -manner and thisconnects the circuit including the tone machine 3 to the calledtelephone, said machine being in continuous operation, as will f now 'bemore fully described.

Whenever the telephone included in the circuit II 'is busy, either byreason of being called or when making 'a call, the private bank wiper I4associated with that telephone isA connected to positive' battery andthrough the wire I5, contact spring I6 of relay Il, spring I8 of relayI9 and connecting wires, a circuit including the winding of the busyrelay I3 is completed to negative battery 20. The relay I1, which isdesigned to release slowly, is energized .in connection with the rotarystep magnet 38 so that the spring I6 closes against its make contact tocomplete the circuit just described. Operation of the relay I3 causesthe spring 5 to close the circuit including the wire 8 and tone machine3 so that the latter, which is in continuous operation, has its tonetransmitted to the line 9, wiper III and line II. and the tone is 'heardmomentarily over` the called telephone. The tone is softened by thecondenser 4 so that it does not interfere with conversation over thebusy line and is immediately discontinued due to the break of the spring6 from the spring y1. The busy relay I3 remains in the energizedcondition until the calling telephon(` disconnects this relay whichoperates only when a busy line contact is encountered by the wipers of aselector circuit. Our special tone circuit does not interfere with thenormal and old function of the busy relay I3 which has a contact spring2| adapted to close a circuit including wires 22 and 23 andthe positivetransmission line 26 whereby a busy tone is transmitted to the callingsubscriber from a busy tone machine, not

shown.

Details of the connector switch circuit illus- Vtrated in the drawingform no part of our invention and such circuits are in general use but abrief description of the operation as far as it relates to ourimprovements follows. When a subscriber calls, his line is extended inthe usual manner through the automatic switches and the transmissioncircuit wires 24 and 25. A circuit is thereby completed for theoperation of the relay 26 from battery and ground through its windings,contacts of relay 28 and the calling sub'- scrib'rrs loop over the tipand ring conduct-or.

The relay 26, by the operation of its spring contactsenergizes relay 30which. prepares the vertical magnet circuit to receive the impulses. Thedial is now turned-and impulses are sent from the calling telephone tocause relay 26 to release a number of times in quick successiondepending on the figure dialed. The relay 30, being slow acting. holdsup during the series of impulses. When the first impulse causes relay 26to fall back, the circuit is closed from plus battery through backcontact ofrelay 26, make contact 34 of relay 30, off-normal springs 33through winding of relay 32 and vertical magnet 3| to minus battery.This elevates the connector shaft one step whereupon the off-normalsprings are released mechanically. These springs now shift theirpositions, the springs 33 and 36 separate and springs 36 and 31 makecontact. When the next or second impulse of the telephone againdeenergizes the relay 26 the circuit is closed from plus battery throughoff-normal springs 36 and 31 through make contact relay 32, winding ofrelay 32 and the vertical magnet to minus .battery. The relay 32 beingslow acting remains energized while the impulses are passing through'its winding. Each succeeding impulse of this series takes the samecircuit and after this series of vertical impulses has been completedrelay 32, receiving no more current, falls back and switches the impulsecircuit from vertical to the rotary magnet 38 through back contact 39. v

The impulses delivered to relay 26 by the dialing of the next digithaving similar effect, except that each time relay 26 falls back itcompletes a circuit from plus battery through its back contact, throughthe make contact 34 of relay 30, off-normal springs 36 and 31, backcontacts of relays 32; I3 and I9 through the rotary magnet.

38 to minus battery. This steps the wipers around in a horizontaldirection.

Relay I1 is connected in multiple with the ro- .tary magnet 38 andreceives a portion of the impulse current delivered by the relay 26during the rotary motion. tary step and being slow acting remainsoperative during the series of rotary impulses. When operated itssprings form a shunt around the back contacts of relay I3 so that incase the latter should operate the rotary magnetcircuit' will not beopened because it is maintained through the make contacts of relay I1.As hereinbefore pointed out, whenever a line is busy the private bankcontact I4 of that line is connected to plus battery so that the busyrelay I3 is energized.

Upon completion of the rotary impulses the relay I1 releasestransferring the circuit of relay I3 from t'he plus battery' on theprivate bank contact to plus battery on the springs of relay 30.

The relay I1 is equipped with make before break'springs so as toaccomplish the transfer of this circuit from the private w-iper to plusbattery of relay 30 without allowing the circuit to be broken.

When the called line is not busy the relay I3 l will not energize but assoon as the relay I1 has released, a circuit -will be closed from minusbattery at the cut-off relay through its winding to .the private contactand private wiper through the back contact of relay I1, the lowresistance winding 40 of relay I9, the back contact of relay I3 to plusbattery at the springs of relay 30. This v'energizes the winding 40 ofrelay I9 giving it suicient power to make its spring contacts 4I.

This connects the high resistance winding 42 to plus battery at thecontact of relay 30 thereby It energizes on the first ro-- rent isfurnished from a ringing generator through circuit wire 44 to theconnector switch and through the low resistance winding of a relay 45,contacts of relays 45 and I9 to the telephone being called, therebyringing the bell of line II. When the called party answers, the removalof the receiver places the transmitter and receiver across' the linewhich allows -the winding of the relay 45 to receive direct current fromthe battery in series with the generator. This operates the armature ofrelay 45 far enough to bring the pair of springs 46 into contact whichcloses the 'system having a line bank wiper and busy relay and it isfound to be idle, relay I9 immediately connects plus battery to theinterrupter equipment (not shown) This equipment operates the generatorcontrol relay so that alternating curcircuit of the high resistanceWinding of the relay 45 frorn minus battery to plus battery at thesprings of relay 30, thus operating the armature of relay 45 in fullstroke, opening the generator and interrupter start circuit, andconnecting the lines of the called telephone through to the windings ofrelay 28which operates.

The transmission circuit of the connector is indicated in heavy lines inthe drawing. It will be understood that battery to the transmitter ofthe calling telephone is fed through relay 26 while battery to thecalled telephone is fed through relay 28. These two circuits areseparated by condensers which provide a path for voice currents to passbetween the two telephones. The spring contacts of the connector throughAwhich the conversation passes are also shown in the drawing. A releasemagnet 41 is provided in acircuit which is normally open at the offcontact springs and when the connector is seized this circuit is alsoopen at the springs of relay 28. The rst vertical step of the connectorshaft operates the off-normal springs to close the release magnetcircuit at that point and makes the release of the connector dependentuponthe replacement of the receivers of both parties. If the callingparty is first to replace the receiver, relay 26I will fall back butrelay 30, being slow acting, remains operative long enough to close acircuit from plus battery at the back Contact of relay 26 through makecontact of relay 30, oit-normal springs and winding of relay I1 to minusbattery. When thus operated, relay I1 disconnects plus battery from therelease trunk 48 and this permits all switches associated with theconnector to release. Relay I1 restores to normal and places plusbattery on the release trunk again from the springs of relay I9. Thisplus battery protects the connector against being selected for anothercall while it is held in this manner-.by the called party. Replacementof the receiver by the called party allows relay 28 to fall back,closing the release magnet circuit and allowing the connector torelease.

Our special tone machine 3 is preferably in continuous operation andarranged to supply the special tone to a large number of special tonecircuits in multiple. The cost of adding such circuits does not exceedabout three dollars per switch and when it is considered that each groupof one hundred lines is served by ve to ten connector switches, it willbe evident that the cost per line is very small.

Having described our invention what we claim as new and desire toprotect by Letters Patent is:

l. The combination in an automatic telephone adapted to be energizedonly when an attempt is made to establish a connection with a busy lineof a circuit connected vto said line bank'wiper and including springcontacts of the make-b efore break type under control of said relay anda constantly operating source of appraising tone 3. In an automaticstep-by-step telephone connector switch having s. line bank wiper and abusy relay adapted to be energized only when an attempt is made toestablish a connection with a busy line, the improvement which comprisesa circuit connected to said wiper, a'set of makebefore-break spring'contacts under control of said relay for closing and breaking saidcircuit and a constantly operating source of appraising tone adapted tobe connected in said circuit under 10 control of said contacts.

BRONSON WEST. HOWARD L. JOHNSON

